The present invention relates to applying a protective coating of an electrical insulating material to the stator windings of a motor or other electrical inductive device.
Although the stator windings of electrical inductive devices, such as motors, as wound with magnet wire having an enamel or other insulative coating thereon, it is often desirable to further coat the windings and seal them from the environment. Small cracks in the wire insulation and other small, localized areas on the wire where the insulation has been worn off will usually not present any problems in normal motor applications. When the motor is used in environments where the stator is exposed to moisture or abrasive materials, such as sand and dirt, it is often desirable to further protect the stator windings from the environment by means of an additional coating. For example, open motors utilized in driving pumps in oil field applications are exposed directly to blowing sand and dirt as well as moisture. Additional protection of the stator windings is also desirable in blower motors utilized in the cooling systems for locomotive traction motors.
The usual material for coating stator windings is a solventless varnish that has a hardener mixed therein so that the varnish will cure at a given elevated temperature, such as 170.degree. C. The present method of application solventless varnish to stator windings comprises energizing the windings with an applied voltage to raise the temperature of the windings to about 95.degree. C. and then applying the varnish with a wand, which is a tube through which the varnish is flowed. Either the stator or the wand may be rotated. The varnish is applied with the wand to the end turns on both ends of the stator core, and the varnish is caused to flow into the slots of the core. The application of the varnish is then discontinued and the windings are energized with a higher current to increase their temperature to 145.degree. C. to gel the varnish and then to 170.degree. C. to cure the varnish.
It has been found that this method does not provide an even distribution of the varnish throughout the winding, particularly in the portion of the winding disposed within the core slots, nor does it provide a continuous coating over the end turns to protect them from the environment in open electrical machinery. Furthermore, the coating of varnish on the end turns is quite thin because the varnish is applied with the end turns at 95.degree. C., which is below the gel temperature of the varnish. Accordingly, the varnish will not build up on the end turns to provide a thicker coating.
It has also been proposed to dip the end turn portions of the windings in a solventless varnish, but again this has been done at a temperature below the gel temperature of the varnish so that only a thin coating of varnish is applied to the end turns.
It is known to coat the stator windings with a protective layer of insulation by immersing the stator within a fluidized bed of powdered insulating material and then resistance heating the windings to melt the powder and adhere it to the windings. U.S. Pat. Nos. 3,244,918; 3,145,127 and 3,710,437 are examples of this type of method. It is also known to encapsulate a stator within an insulating resinous material by dipping part of the stator and windings in a bath of thick resinous coating material, curing the material, then impregnating the entire stator with a thin resinous material, curing that material and then immersing the other portion of the stator in the thick material to completely encapsulate the same. This type of method is disclosed in U.S. Pat. No. 2,414,525.